By way of introduction, Differential Power Analysis (DPA) includes a class of attacks against devices such as, smart cards and secure cryptographic tokens, by way of example only. DPA attacks typically exploit characteristic behavior of transistor logic gates and software running on smart cards and other cryptographic devices, by way of example only.
The DPA attacks are typically performed by monitoring the electrical activity of a device, then generally using statistical methods to determine secret information (such as secret keys and user PINs, by way of example only) in the device.
The following references are also believed to represent the state of the art:                U.S. Pat. No. 6,298,442 to Kocher, et al.;        US Published Patent Application 2005/0073346 of Elbe, et al.;        US Published Patent Application 2006/0125664 of Liardet, et al.;        US Published Patent Application 2007/053683 of Hwang;        US Published Patent Application 2008/0019503 of Dupaquis, et al.;        US Published Patent Application 2009/0010424 of Qi, et al.;        PCT Published Patent Application 2006/053683 of ARM Limited;        A book entitled “Power Analysis Attacks: Revealing the Secrets of Smart Cards” by Mangard, E. Oswald, and T. Popp, published by Springer 2007;        “Power Analysis” described by wikipedia.com;        An article entitled “DPA Countermeasures” posted at www.cryptography.com/resources/whitepapers/DPA.html; and        An article entitled “Licensed Countermeasures” posted at www.cryptography.com/technology/dpa/licensing.html.        